Here is a little history and background before I begin. I have a 1998 Z-24 that I bought new and used as my DD and autocross car for about 4 years. After that I got into HPDE track events where you drive your car on a real road course as fast as possible. After bending the backing plates into a \___/ shape at my second track event I decided it was time for a brake upgrade. I looked into the OTS kits by Baer, Wilwood, etc, but all of them were just too much coin for my wallet. I decided to buy all the components and make my own.
The first question was which caliper? The PBR unit that Baer uses was very popular as it was used on the late 90’s Corvette, Z-28, and Cobra so that seemed like a good place to start. I found several caliper sets (new) for the Cobra on Ebay for a reasonable amount, not cheap, but still reasonable. After a little more digging I discovered that though the calipers between these cars look the same, they were not. To best match the J-body’s stock hydraulics, the caliper with twin 38mm pistons is what I needed. The Cobra calipers switched piston sizes depending on the year and the later models had twin 40.5mm pistons, which were the new ones being sold on Ebay and by Ford Motorsport. I really needed the correct piston size so I continued the search for used calipers.
While searching for the calipers I decided to dig into the rotor research. I did lots of measuring and talked to Todd over at TCE Performance Products about getting a custom 2-piece rotor setup from him. I decided on the 12.2” x 1.1” version with the aluminum hat which was machined to match the stock 57.1mm hub. These were damn expensive ($600 per pair) but I figured they’d last forever so why not. Nothing lasts forever…read on.
The reason I went with a 2-piece custom rotor was two-fold. First was after getting my rear rotors (stock Corvette 12” ones) drilled to match the 5x100 pattern I learned that @!#$ was high dollar. I knew if I had to get new front rotors often I’d go broke re-drilling them. With the two piece setup all I’d have to do is buy new rotor discs and bolt them onto the hats. Second was the offset of the hat could be almost anything I needed. It’s a balancing act between hitting the ball joint in back or the wheel’s spokes up front. I figured out what I needed and had the hats made to spec.
A friend turned me onto buying used parts from the guys over at Corvette Forums. A lot of C4 guys upgrade their brakes to the newer better C5 design and sell off their old stuff to lots of F-body guys. I logged on and found a seller who was getting rid of all (4) of his stock calipers of his ’95 ZR-1. The ZR-1 and GS models both had the J55 HD setup which is what I wanted. The J55 package had 38mm pistons and used 13” x 1.1” rotors. I bought the calipers from the guy and proceeded to fit-up.
Here’s the long story made short…really quick. After getting some pics of the machined spindles Wild Weasel got from Baer, I modified my spindles and installed everything on the car. I used this setup on track for 2 years and the car stopped like a mofo. So what’s the problem right? Well those “last forever” rotors turned out to last a maximum of 3 event weekends. At $300 per pair to replace the front rotors that @!#$ started to add up REALLY quick. Time for homemade BBK version 1.1 read on.
I have a friend that tracks a Z06 who gets rotors for $39 each at NAPA. When they crack (after about 3 events) he just buys a new pair. They are so cheap it just doesn’t matter. I decided that I needed to do whatever it took to use an OTS Corvette rotor with my setup. I knew the OTS C4 Corvette rotor’s hat was deeper than my current ones so I’d need to start over with another pair of spindles. To save that kind of money in rotors it would worth it.
After more research, I discovered that there was yet another version of the PBR caliper. I have the J55 setup which again was designed to work with the HD 13” x 1.1” rotor. The stock Vette used the JL9 setup which has a caliper with a throat that is more shallow for use with the STD 12” x .81” rotor. Since I already had the J55 calipers, I needed to stick with the 1.1” thk rotor which was 13”, not 12.2” like I had in BBK version 1.0.
A little more digging turned up the Cobra used 13” x 1.1” rotors as well and the hat depth was closer to what I needed. In addition the Cobra rotor was $10 cheaper per, which was an added bonus. I bought one (yeah the guy at the counter was puzzled when I got just one) to use for fitment in BBK version 1.1. I left and was off to the junkyard to find another pair of spindles which I purchased for less than $50.
Now I have a spindle (with hub assembly) 13” rotor, and my J55 PBR caliper ready to do some fabrication. First up the rotor bolt pattern. The Cobra uses 5 x 4.5 (IIRC) and I need 5 x100. Unlike before, the light came on in my head as I said to myself “hey, the holes don’t need to be perfectly centered, they just need to be close and fit the stock hub’s studs”. The reason is that the hub is what center’s the rotor, not the bolts! I made a simple paper template on the computer at work, printed it, cut it out, and taped it to the rotor. I then used a drill to make 5 new holes in between the existing ones. Ok now you say, does the Cobra have a 57.1mm hub? Of course not! That would just be too damn easy. The Cobra’s hub is 70.5mm (again IIRC) so I ordered a pair of aluminum adapter rings to make the two match. Expensive rotor problem solved.
Next it was time to modify the spindles to work with the new rotor. (Keep in mind that this was my 2nd time EVAR working with metal. I’m pretty good with wood, but metal work was new to me). Since I had done this one time before in BBK version 1.0 I had some idea of what needed to be modified on the spindles, but all the work still had to be done.
The pictures below show an overview of the process of modifying the spindles. I used a simple pneumatic side grinder, electric skill saw with a metal cutting blade, and drill. I did all the fitment using trial and error until it all worked. Once the first one is done the second one takes literally half the time. Took me about a weekend this time around.
If you throw out the cost of R&D I used in making BBK version 1.0 it’s quite affordable at less than $350. My loss is your gain as I learned everything the hard way. Also keep in mind that the popular Baer kit (which is quite similar) uses the JL9 caliper (not the HD J55) with 0.81” thk rotor so you can’t exactly compare apples to apples cost wise here. My setup is designed for extreme use ON A RACE TRACK. It’s NOT FOR SHOW; it’s made to stop my car repeatedly from 110 MPH+ during a 25 min track session. Thicker rotors give more hear dissipation and that is what I needed. Here’s a basic cost breakdown less the SS brake lines:
(2) Used GM J55 calipers and brackets ($100)
(2) Used Stock J-body spindles ($50)
(2) 13” x 1.1” Cobra rotors ($60 at NAPA)
(2) Adapter rings ($30 + $50 machining = $80)
(2) Steel plates ($10)
(4) Bolts ($10)
(2) Pipe couplings ($5)
(1) Spray paint ($5)
-Vincent K.
1998 Z-24
www.thscc.com
http://www.j-body.org/members/vkz24/
"Racecar spelled backwards is still Racecar"
